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<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>网页计算器</title>
    <style>
            a:link,a:visited{
                color: #222;text-decoration: none;}
           a:hover{color: #fd4913;}
       </style>
   
</head>
<body>
    <h2>网页计算器</h2>
    <p>整数1：<input id="num1" type="text"></p>
    <p>整数2：<input id="num2" type="text"></p>
    <p>
        <input type="button" value="相加" onclick="calc(add)">
        <input type="button" value="相减" onclick="calc(sub)">
        <input type="button" value="相乘" onclick="calc(mul)">
        <input type="button" value="相除" onclick="calc(div)">
    </p>
    <p>结果：<input id="result" type="text" readonly></p>
    <script>
       function calc(func){
           var result=document.getElementById('result');
           var num1=parseInt(document.getElementById('num1').value);
           var num2=parseInt(document.getElementById('num2').value);
           if(isNaN(num1)||isNaN(num2)){
               alert('请输入数字');
               return false;
           }
           result.value=func(num1,num2);
       }
       function add(num1,num2){
           return num1+num2;
       }
       function sub(num1,num2){
           return num1-num2;
       }
       function mul(num1,num2){
           return num1*num2;
       }
       function div(num1,num2){
           if(num2===0){
               alert('除数不能为0');
               return ' ';
           }
           return num1/num2;
       }
    </script>
    <p><a href="default.html">返回目录</a></p>
    <p><a href="第四章.html">返回第四章</a></p>
    <p><a href="第五章.html">下一章</a></p>
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